The invention concerns an electroplating barrel having a perforated barrel shell with a peripheral barrel opening which can be closed by a lid, and with a cylindrical peripheral shape of non-circular cross-section, and being formed from a plurality of perforated plastic shell elements having a square shape when projected onto a plane, radially with respect to the barrel axis a-a, and which are each connected to another by one longitudinal rib at their longitudinal sides extending parallel to the barrel axis a-a.
In electroplating barrels of this type, each longitudinal side of the plastic perforated shell elements, which form the barrel shell, is welded to one longitudinal plastic rib, each extending in the axial direction of the barrel. Usually, the polygonal barrel shell has a hexagonal cross-section and the longitudinal edges of the shell elements must be correspondingly bevelled to be welded over a large area to the longitudinal connecting rib (see DE-OS 30 19 719 A1).
The production of such a barrel shell is therefore time-consuming since the longitudinal ribs must be butt welded along each of their longitudinal sides to one shell element using heat reflectors, requiring two welding processes for each longitudinal rib.
This barrel construction has the serious disadvantage that barrel volumes of different sizes require shell elements with correspondingly differentiated transverse front ends.
It is therefore the underlying purpose of the present invention to provide an electroplating barrel, which does not require the usual welding processes for mutual connection of their shell elements, and which permits modification of the volume of the barrel shell to a certain degree without adjustment of the transverse front end size of the shell elements or with shell elements of the same width.
This object is achieved in accordance with the invention in that each longitudinal rib is formed by two rib-shaped projections, which are connected to each other through gluing or cold welding, which are attached to a longitudinal side of a neighboring shell element, and which define an outer rib surface, wherein the outer rib surface subtends an angle xcex1 whose legs intersect on the barrel axis a-a and whose angular size is defined by a number of shell elements which are to be rigidly connected to one another, wherein the cross-section of the rib-shaped projections is such that the angle xcex1 can be changed appropriately for producing an electroplating barrel having a different number of shell elements through machining of the outer rib surfaces.
The longitudinal rib connecting the two neighboring shell elements of this barrel construction is divided into two rib-shaped projections which are each formed on one of the two longitudinal sides of the shell elements. Connection of the rib-shaped projections of neighboring shell elements can therefore be realized in one single working step through gluing or so-called cold welding (application of a solvent for dissolving the plastic material), wherein conventional bevelling of the longitudinal edges of the shell elements in connection with a longitudinal rib can be completely omitted.
The cross-section of the rib-shaped projections is thereby selected such that the barrel shells can be produced with different cross-sections or cross-sectional shapes. The cross-section of the rib-shaped projections or of the angles defined by the outer surfaces of these ribs is selected such that lateral joining of shell elements produces a desired barrel shell size, as defined by e.g. seven shell elements.
If barrel shells are to be produced having a smaller number of shell elements or with correspondingly smaller volume, only the outer surface of the rib-shaped projections must be changed e.g. by milling, to correspondingly increase the angle which they define.
The invention therefore permits mutual orientation of shell elements of identical cross-section at different angle settings to permit production of barrel shells of different cross-sectional shapes from identically formed shell elements, wherein the initial shape of the shell elements may be such that machining of the rib-shaped projections permits assembly of barrel shells with a smaller or larger number of shell elements.
In a preferred embodiment of the insertion, the rib-shaped projections form longitudinal ribs projecting outwardly from the barrel shell which are interconnected across an entire rib height. This has the advantage that they can be clamped together, using a clamping device, for mutual connection using a glue or a solvent for softening the outer surface of the ribs to achieve a homogeneous mutual connection.
Advantageously, the outer surfaces of the ribs of each shell element of a barrel shell design in accordance with the invention subtend an angle of approximately 60xc2x0 which converges in the direction of the barrel interior. This is advantageous for applying a clamping tool to clamp neighboring rib-shaped projections.
To avoid indentations in the outer surfaces of the ribs of the shell elements produced during injection molding, provision of a channel in the rib-shaped projections is proposed which produces favorable wall thicknesses for the rib-shaped projections. In this embodiment, the rib-shaped projections have a substantially rectangular cross-section and can be penetrated in the longitudinal direction by a channel whose cross-sectional shape matches the cross-section of the longitudinal ribs. In a further development of the rib-shaped projections a sealed metal core is inserted into the channel. This guarantees that these cannot yield during mutual clamping.
The perforated wall of the shell elements may be flat. In a preferred design, the perforated wall part of the shell elements, which is disposed between the rib-shaped projections, is outwardly curved about an axis which is parallel to the barrel axis a-a. The outwardly curved wall is advantageous in that the barrel content optimally passes closely by the anode of the electroplating bath during rotation of the barrel. In addition, flat parts which are to be electroplated are thereby prevented from sticking to the inside wall of the shell elements.
The convex wall curvature in connection with the rib-shaped projections formed on the side of the shell elements produces rib-like elevations on the inner circumference of the barrel along each shell line to ensure good material circulation.
In one shell element design, transverse braces are formed on the outside of the shell elements, which bridge the separation between the rib-shaped projections of the shell elements. Each front end of the shell elements can be flush with one of the transverse braces. This is advantageous in that the perforated wall can be produced with appropriately small thickness and less material thereby providing sufficient stability.
The thickness of the transverse braces is advantageously selected such that the shell elements can be separated along a transverse center of a brace. Joining and homogeneous connection of the front ends of the shell elements, and optionally of an appropriately shortened shell element, in the direction of the barrel axis permits production of barrels of desired, stepped lengths, wherein shell elements of identical format can always be used together with only one, appropriately shortened, shell element.
The maximum length of the shell elements will thereby advantageously be selected such that their length can accommodate the smallest barrel length of a barrel production program.
The perforation of the shell elements is advantageously in the form of a slit, wherein the slits are preferably placed at separations from one another. A slitted perforation of this type has a particularly favorable effect on the electron flow during electroplating when the slits extend in the circumferential direction of the barrel.
In accordance with a preferred embodiment of the invention, the shell elements are formed in one piece from polymer (PUR). The perforated wall part of the shell elements can be formed from polymer (PUR) and their lateral rib-shaped projections from another thermoplastic material. Either the complete shell elements or merely their perforated wall part can be injected from a polymer to guarantee long service life. In the latter case, their lateral rib-shaped projections can be produced from a less expensive thermoplastic material, preferably polypropylene or polyethylene. The cross-section of the wall part and rib-shaped projections must then be such that the rib-shaped projections can be injected with the wall part in a form-locking fashion. Combination of different thermoplastic materials, such as e.g. polymer (PUR) and polyethylene for rib-shaped projections and perforated wall parts of the shell elements is generally regarded as advantageous for electroplating barrels.
The combination of the above-mentioned plastic materials has the following advantage:
Electroplating barrels are usually produced from only one single plastic material, i.e. polypropylene or polyethylene. This has the disadvantage that the perforations in the barrel shell narrow or become largely blocked after a period of time due to the presence of small particles or objects circulating in the barrel, which often have sharp edges. The present combination of plastic materials eliminates this severe disadvantage of the electroplating process.
In a further embodiment of the invention, the plastic barrel front walls are formed of sector-shaped front wall parts which are sidewardly connected to one another through gluing or cold-welding and form together a central bearing hub. This permits advantageous production of relatively large barrel front wall surfaces using a relatively small injection mold, which can be produced at low cost. Formation of the sector-shaped front wall from a number of sector-shaped front wall parts which corresponds to the number of shell elements, is advantageous in that each of their lateral rib-shaped projections can be made to coincide with one front surface of the longitudinal ribs of the barrel shell formed by the lateral rib-shaped projections and connecting thereto when gluing or cold welding each barrel front wall to a front end of the barrel shell.
In a preferred construction of the front wall parts, the sides of the front wall parts have an integrally formed rib-shaped projection, and neighboring rib-shaped projections are glued or cold-welded to form a longitudinal rib, wherein the longitudinal ribs project radially outwardly beyond the front wall parts at the barrel periphery and cover longitudinal ribs formed by the rib-shaped projections of the shell elements at the front end of the barrel. Analog to the shell elements, the rib-shaped projections can be formed of the same plastic material or of a different thermoplastic material than the front wall parts.
The proposed design of the barrel front walls is particularly advantageous when they are perforated over at least a portion of their wall surface. In this case, the injection tool must only be provided with corresponding projections for forming perforations throughout a relatively small surface region.